Fluid entrapment detection

ABSTRACT

A washing machine includes a cabinet, a wash tub supported within the cabinet, a spin basket for holding a wash load, the spin basket rotatable in the wash tub by a motor, and a controller for driving the motor to rotate the spin basket. The controller is adapted to detect water entrapment within a wash load in a spin basket of a washing machine by measuring a first parameter indicative of the rotational inertia of the spin basket when accelerated to a first spin speed, controlling the spin basket to dewater a wash load in the spin basket, measuring a second parameter indicative of the rotational inertia of the spin basket at the first speed, comparing the first and second parameters, and detecting whether there is water entrapped in the wash load based on the comparison between the first and second parameters.

CROSS-REFERENCE AND INCORPORATION BY REFERENCE

This application is a non-provisional of U.S. Provisional PatentApplication Ser. No. 60/887,390, entitled “Fluid Entrapment Detection”,filed Jan. 31, 2007. U.S. Patent Provisional Patent Application Ser. No.60/887,390 is hereby incorporated by reference.

FIELD OF INVENTION

The present invention relates to washing machine, and in particular to acontrol system used to modify the operation of the washing machine basedon certain characteristics of the wash load.

BACKGROUND TO THE INVENTION

The typical washing machine has a washing basket, tub or receptacle thatholds laundry for washing. The washing basket is coupled to a motor thatis used to rotate the washing basket at various speeds during variousoperating cycles of the washing machine. A controller is used to controlthe operation of the motor depending on the various cycles of thewashing cycle. Similarly, the controller receives feedback from a numberof sensors and/or uses a number of algorithms to sense a number ofconditions within the washing drum. This feedback is used to control theoperating speed of the motor depending on the various operatingconditions sensed during the washing cycle. Such conditions include washbasket imbalance conditions for example. This condition is predominantlysensed when the wash basket speed is being changed, for example, from anagitation cycle up to optimal spin speed where wash load dehydrationoccurs. As an example, an imbalance in the washing basket due to theload size and/or load distribution within the wash basket is magnifiedwhen the wash basket is rotated at high speeds. This will causeexcessive vibration and may lead to washing machine malfunction.

US2005/0155159 to Gregory A Peterson discloses a method of operating awashing machine to detect a drum unbalance condition during the washingmachine spin cycle. The washing machine is operated at fast speed torotate the laundry basket. Load balance data is collected during therotation of the basket. The received load balance data is then analysedand the washing machine is operated at a second high speed if it isdetermined that the load in the receptacle is balanced. This systemincludes a number of sensors which detect vibration of the washingmachine drum to provide feedback to a controller which then analyses thedata and modifies the operation of the washing cycle based on theinformation received from the sensors.

In this specification where reference has been made to patentspecifications, other external documents, are other sources ofinformation, this is generally for the purpose of providing a contextfor discussing the features of the invention. Unless specifically statedotherwise reference to such external documents is not to be construed asan admission that such documents or such sources of information, in anyjurisdiction, are prior art, or form part of the common generalknowledge in the art.

It is an object of the present invention to provide a washing machine ormethod for detecting water entrapped in a wash load.

SUMMARY OF THE INVENTION

In a first aspect, the present invention may broadly be said to be awashing machine comprising:

a cabinet,

a wash tub supported within the cabinet;

a spin basket for holding a wash load, the spin basket rotatable in thewash tub by a motor,

a controller for driving the motor to rotate the spin basket, thecontroller adapted to detect water entrapment within a wash load in aspin basket of a washing machine by:

measuring a first parameter indicative of the rotational inertia of thespin basket when accelerated to a first spin speed,

controlling the spin basket to dewater a wash load in the spin basket,

measuring a second parameter indicative of the rotational inertia of thespin basket at the first speed,

comparing the first and second parameters, and

detecting whether there is water entrapped in the wash load based on thecomparison between the first and second parameters.

In a second aspect, the present invention may broadly be said to be amethod of detecting water entrapment within a wash load in a spin basketof a washing machine, comprising the steps of:

measuring a first parameter indicative of the rotational inertia of thespin basket when accelerated to a first spin speed,

dewatering the wash load,

measuring a second parameter indicative of the rotational inertia of thespin basket at the first speed,

comparing the first and second parameters, and

determining whether there is water entrapped in the wash load based onthe comparison between the first and second parameters.

When interpreting statements in this invention which include“comprising”, the features prefaced by that term in each statement, allneed to be present but other features can also be present.

This invention may also be said broadly to comprise in the parts,elements and features referred to or indicated in the specification ofthe application, individually or collectively, and any or allcombinations of any two or more of said parts, elements or features, andwhere specific integers are mentioned herein which have knownequivalents in the art to which this invention relates, such knownequivalents are deemed to be incorporated herein as if individually setforth.

The invention comprises the foregoing and also envisages constructionsof which the following only gives examples.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred form of the present invention will now be described by wayof example only and with reference to the accompanying drawings.

FIG. 1 shows in schematic form a washing machine according to oneembodiment of the invention,

FIG. 2 shows in schematic form a wash load being engulfed by awaterproof item within the wash basket process of FIG. 1.

FIG. 3 shows in schematic form the position within a spin basket of awash load engulfed by a waterproof item when the wash basket is spun.

FIG. 4 is high level process flow showing how the wash load inertiasensing testing is applied during a typical wash cycle.

FIG. 5 is a process flow diagram showing one step of the wash loadinertia sensing method.

FIG. 6 is a process flow diagram showing the implementation of the washload inertia sensing as applied to the washing machine in FIG. 1.

DETAILED DESCRIPTION Overview

The present invention will be described primarily with reference to alaundry washing machine. It has been found that if water is trappedinside a large waterproof item for example that surrounds or enclosesaround a number of other clothes items in the wash basket being cleaned,it is possible for the machine can reach a high spin speed, for exampleover 600 rpm, before the wash basket is forced violently out of balance.This type of situation is caused by water being trapped by thewaterproof item and can result in the washing machine being damaged.

FIG. 1 shows in schematic form a washing machine 10 adapted to modifyits operation based on the type or nature of a wash load 14 in thewash/spin basket 13. The washing machine 10 comprises an outer housing11, an internal tub 12 and a spin basket 13 within the inner tub 12. Thespin basket 13 is adapted to hold and wash items comprising the washload 14. The washing machine 10 includes a motor 15 for an agitator 19in order to wash the items in a wash load. A pump is required forrecirculating water and delivering water from the spin basket. A motoris provided for introducing water into the wash tub 12. The machine alsoincludes a controller 16 which is adapted to control various aspects ofthe function of the washing machine 10, including the motor 15 and pumpfor filling and draining wash water from the spin basket 13. Thecontroller can also operate various other functions of the washingmachine. These functions will be known to those skilled in the art andwill not be described here.

Water Entrapment Condition

For a normal wash load it has been found that the inertia after spinningthe wash load to 330 rpm for the first time should be noticeably lessthan the measured inertia straight after draining the wash water out ofthe wash load. This is due to water being extracted from the clotheswhile spinning the wash load at low speed. It has been found that a washload would typically lose approximately 30% of its saturated mass afterspinning the wash load to 330 rpm. However, if a waterproof item hasengulfed the rest of the wash load thereby preventing water fromescaping, then the water remaining in the wash bowl will be centrifugedoutwards during spinning phase thereby increasing the rotationalinertia. Water can also be trapped due to clogging of the spin basket(due to calcium deposits or the like). This can also cause imbalanceissues. The present invention can alleviate this also by doing inertiatesting and limiting spin speed if necessary.

A preferred embodiment of the invention will be described with referenceto FIG. 2. This embodiment relates to a washing machine 10 with a lowprofile wash-plate 19 that has a mode that is part of the wash cycleprocess that determines if wash water 18 is being trapped within thespin basket 13.

It has been found that after draining the wash water 18 from the spinbasket 13, excess wash water 18 can be trapped in the wash load 14. Thishas been found to be more likely to happen in a washing machine with alow-profile wash plate. FIG. 2 shows this particular condition whereby awaterproof item 40 has engulfed the rest of the wash load 41 therebypreventing all of the wash water from being drained from the wash load41 and exiting the spin basket 13. Under these conditions, when thecontroller 16 initiates a spin cycle, the wash load items 41 that haveretained the wash water are forced towards the circumference of the spinbasket 13 due to the centrifugal force acting on the wash load 41 asshown in FIG. 3. An amount of the wash water will remain trapped in thewash load 41 during the spin cycle as a result of the waterproof item 40engulfing the wash load 41 thereby preventing the excess water frombeing allowed to be removed and subsequently drain away from the washload 41.

Hence, it has been found that when the spin basket 13 is spun up to acritical spin speed, the entrapped water within the wash load 41suddenly shifts position within the wash bowl 13 causing a sudden andviolent off-balance condition. This sudden shift of the entrapped wateris believed to be due to the entrapped water being held by the wash load41 in temporary “baffles” that compress against the walls of the spinbasket 13 as the spin basket 13 accelerates up to spin speed. At thecritical spin speed, the “baffles” compress enough to allow the water tooverflow them.

In this off-balance condition, the controller 16 will not continue tospin the spin basket 13 up to a maximum spin speed. The excess out ofbalance condition has been found to be so violent that the machine is atrisk of being damaged if the spin cycle is not limited. As an example,this violent off-balance condition can cause damage to the washingmachine suspension (not shown). It has been found that this suddenoff-balance condition can occur when the spin speed reaches between 600rpm and 1000 rpm. By limiting the spin basket spin speed to below acritical spin speed when an entrapped water condition has been detected,the sudden off-balance condition can be prevented. Typically, thecritical spin speed has been found, through experimentation, to be nogreater than 670 rpm.

The present invention is therefore directed to a system that canincorporated into a clothes washing cycle that can be used to detectwhen water within the wash load has been entrapped and subsequentlylimit the spin speed to below a threshold value for the remainder of thewashing cycle.

Through experimentation it has been found that the most robust techniquefor detecting a water entrapment condition is based on a system that iscapable of measuring the rotational inertia of a wash load when the washload is placed into a spin condition. Furthermore, given that the out ofbalance condition has been found to occur at above a certain criticalspin speed, it is preferable that the system employs a low speedrotational inertia detection system.

Rotational Inertia Detection

The more rotational inertia an object has, the less the object respondsto being spun. In other words, the rotational inertia of an object is ameasure of the object's resistance to a change of rotation. The lowspeed rotational inertia detection of a preferred embodiment of thepresent invention involves a wash load inertia sensing test beingundertaken one or a number of times during each of the drain/spinsequences using the controller 16 to record and analyse the measureddata. The spin basket/wash load rotational inertia is measured beforedewatering of the wash load and is again measured again after dewateringhas occurred. The relationship between the measured rotational inertiavalues before and after dewatering can be used to detect for waterentrapment. For example, if the rotational inertia before dewatering isless than that after dewatering, it can be determined that water isentrapped in the wash load. This measured data is typically ameasurement of the time taken for the spin basket 13 to decelerate froma first higher spin speed to a second lower spin speed when norotational torque is applied by the motor 15 or other driving means.This measured data is recorded and stored in a memory device within thecontroller 16 one or more times during the wash load inertia sensingtest sequence. The controller 16 then analyses the measured data todetermine if water is being entrapped within the wash load 41. If thecontroller 16 determines that water is being entrapped, the controller16 can modify the spin cycle to below a pre-determined threshold speed.This could be in any number of ways. Alternatively, another action maybe taken such as stopping the cycle and issuing an alarm. This wash loadinertia sensing test could be repeated during each drain/spin cycleundertaken throughout the entire wash cycle.

FIG. 4 shows a high level process flow showing how the wash load inertiasensing system testing incorporated in a typical wash cycle used in awashing machine. After the start of the wash cycle at step 90, the spinbasket 13 is filled to a pre-determined water level at step 91 beforethe spin basket 13 is agitated at step 92 to wash the wash load ofclothes. The spin basket 13 is then drained at step 93 before the washload inertia sensing and detection process is undertaken at step 94.Depending on the result of the wash load inertia test at step 95 willdetermine the speed at which the spin basket 13 is to be rotated atduring the spin cycle at step 96. Each step of the wash cycle from step91 through to step 97 is repeated until the last spin cycle isundertaken step 97 after which the wash cycle is completed at step 98.

Wash Load Inertia Sensing Test Sequence

FIG. 5 shows a process flow diagram illustrating each of the wash loadinertia sensing test steps. On completion of an agitation and drainphase of the wash cycle, a wash load inertia test is undertaken. Thistest sequence is undertaken one or more times before a spin speed forthe particular wash load is determined. The entire inertia sensing testsequence is illustrated and discussed later.

For each inertia sensing test, the spin basket 13 is driven by the motor15 up to a spin speed of preferably 45 rpm, step 50 and held at thatspeed for a period in the order of 2 seconds, step 51. Power is thenremoved from the motor 15 thereby allowing the spin basket 13 todecelerate, step 52. The motor 15 uses Hall effect sensors to providerotor position sensing and rotor speed data as a data input to thecontroller 16. Whilst it is preferable to use Hall effect sensors tosense the rotor position other known techniques can be used such as backEMF sensing can also be used. Under the control of the controller 16, atimer integral with the controller 16 is started when the motor 15drives the spin basket 13 by applying a torque. A first spin speed of 45rpm has been determined as suitable but other spin speeds could be usedwithin the range of between 15 rpm to 150 rpm. The idle state isconsidered to occur when the spin basket 13 rotation speed falls below asecond speed such as 15 rpm or less at step 53. The time it takes forthe spin basket 13 to decelerate from preferably 35 rpm or any othersuitable speed less than or equal to the first spin speed of 45 rpm,down to 15 rpm is stored in a memory device within the controller 16 asa first timing value. Whilst it is preferable to time the decelerationof the spin basket 13 between 35 rpm down to 15 rpm, this range shouldbe in no way limiting as other spin speed ranges could be used such asbetween 75 rpm to 20 rpm for example. The spin basket 13 is then allowedto continue to decelerate until the spin basket 13 and the motor 15stops at step 54. The inertia sensing test is repeated again at step 55.A second timing value is obtained by repeating steps 50 through to 54.The controller 16 then retrieves the first timing value from the memorydevice and undertakes an averaging calculation on the first timing valueand the second timing value to provide an averaged timing value as shownin step 56. The averaged timing value is then stored by the controller16 in the memory device as a reference timing value. This provides afirst parameter which is a parameter indicative of the rotationalinertia of the spin basket 13/wash load 41 prior to at least partialdewatering. As will be appreciated by those skilled in the art, morethan two timing values could be measured and averaged to obtain thefirst parameter indicative of the rotational inertia.

Entire Rotational Inertia Protection and Measurement

On completion of the wash load inertia sensing test sequence detailedabove, the spin basket 13 is allowed to spin up to a speed of 330 rpmfor approximately 30 seconds. This provides some dewatering of the washload 41. Power is then removed from the motor 15 allowing the motor 15to coast down to zero rpm indicating that the spin basket 13 has stoppedspinning. The controller 16 then initiates a further wash load inertiasensing test sequence as illustrated with reference to FIG. 4.

The spin basket 13 is driven by the motor 15 up to a spin speed ofpreferably 45 rpm, step 50 and held at that speed for a period in theorder of 2 seconds, step 51. Power is then removed from the motor 15thereby allowing the spin basket 13 to decelerate, step 52. The motor 15uses Hall effect sensors to provide rotor position sensing and speeddata as a data input to the controller 16. Whilst it is preferable touse Hall Effect sensors to sense the rotor position other knowntechniques can be used such as back EMF sensing can also be used. Underthe control of the controller 16, a timer that is integral with thecontroller is started when the motor 15 drives the spin basket 13 byapplying a torque. A speed of 45 rpm has been determined as suitable butother spin speeds could be used within the range of 15 rpm to 150 rpm.The idle state is considered to occur when the spin basket 13 rotationspeed falls below a second speed such as 15 rpm or less at step 53. Thetime it takes for the spin basket 13 to decelerate from 35 rpm down to15 rpm is stored in a memory device within the controller 16 as a firsttiming value. The spin basket 13 is then allowed to continue todecelerate until the spin basket 13 and the motor 15 stops at step 54.The inertia sensing test is repeated again at step 55. A second timingvalue is obtained by repeating steps 50 through to 54. The controller 16then retrieves the first timing value from the memory device andundertakes an averaging calculation on the first timing value and thesecond timing value to provide an averaged timing value as shown in step56. The averaged timing value is then stored by the controller 16 in thememory device as a second reference timing vale. This provides a secondparameter which is a parameter indicative of the rotational inertia ofthe spin basket 13/wash load 41 after a dewatering cycle has occurred.

The controller 16 then retrieves the first reference timing value fromthe memory device and compares the second reference timing value withthe first reference timing value, that is, the second parameter iscompared with the first parameter. Where the second reference timingvalue is greater than the first reference timing value indicates thatthe rotational inertia after dewatering is higher than the rotationalinertia before dewatering indicating that water entrapped within thewash load. If this is the case, a water trapped flag is set to “1” bythe controller 16 and the controller 16 will subsequently limit the spinspeed to not exceed a critical value. This critical spin speed value istypically in the range of between 500 to 700 rpm. If the secondreference timing value is less than the first reference timing value,the water trapped flag is set to “0” by the controller 16 allowing themotor 15 to be driven up to a maximum spin speed that is typically inthe order of 1000 rpm.

The differential method, whereby first and second reference timingvalues are obtained eliminates friction from the analysis whichsimplifies the process.

FIG. 6 show an entire wash cycle for a washing machine that incorporatesthe wash load inertia sensing and detection of the present invention. Inthis embodiment, two inertia sense tests are done to determine the finalspin speed, one as part of the spray rinse cycle, and one as part of thedeep rinse cycle (if there is one). The inertia sensing test is redoneafter a deep rinse because there is a chance that the water gets trappedduring the deep rinse although it may not have happened during the wash.On commencement of the wash cycle at step 60, the spin basket 13 isfilled with water to a predefined water level at step 61 and a firstwash cycle, shown as an economy wash cycle at step 62 is undertaken.More water is added to the spin basket 13 at step 63 prior to thecommencement of a wash load agitate cycle at step 64. The spin basket 13is then drained at step 65 prior to the commencement of the firstinertia sensing and detection process being undertaken at step 66 toprovide the first reference timing value. This is determined as set outabove. A first spray rinse cycle is then undertaken at step 67 beforemotor torque is removed allowing the spin basket to coast to a stop atstep 68. Dewatering is included as part of the spray rinse cycle, step67. Once the spin basket 13 has stopped rotating (after dewatering) thesecond step of the inertia sensing and detection is undertaken at step69 enabling the second reference timing value to be determined (as setout above). A comparison of the first and second reference timing valuesis undertaken at step 70. If the second reference timing value isgreater than the first reference timing signal then a flag is set to onewhich will cause the final spill speed to be limited to 670 rpm orlower. If second reference timing value is less than the first referencetiming value the flag is set to zero which will cause the final spinspeed not to be limited. The remainder of the rinse and drain steps areundertaken at step 71 until the spin basket 13 is dewatered. If one ofthe rinse steps was not a deep rinse at step 72 then the final spinspeed of the spin basket 13 is limited to at or below the critical spinspeed of between 500 to 700 rpm as shown at step 73 before the washcycle is completed at step 74.

In the event that one of the rinse steps was a deep rinse at step 72, ifthe final spin speed is less than between 500 to 700 rpm, shown as 670rpm by way of example in FIG. 6, the spin basket 13 is limited to at orbelow the critical spin speed of 670 rpm or within the range of between500 and 700 rpm as shown at step 73 before the wash cycle is completedat step 74. However, if the final spin speed is determined to be greaterthat the critical speed shown as 670 rpm in step 75 then a furthersecond inertia sensing and detection step is undertaken at step 76 todetermine a second reference timing value (as set out above). The spinbasket is then spun up to a speed of 330 rpm at step 77, motor torque isremoved and the spin basket 13 is again allowed to coast to a stop atstep 78. A further inertia sensing and detection test is undertaken atstep 79 to provide a post dewater reference timing value parametervalue. The controller 16 undertakes a second comparison test todetermine if the second reference timing value is greater or less thanthe post dewatering reference timing value to provide a second parameterat step 78. The controller 16 then compares the first parameter with thesecond parameter to determine if water is entrapped at step 80 todetermine if the spin basket spin speed is to be limited to a criticalspin speed shown as 670 rpm at step 73 before the wash cycle iscompleted at step 74.

A number of tests were undertaken on different load sizes and fabrictypes implementing the wash load inertia sensing test as detailed above.To simulate a waterproof item engulfing a wash load, the wash load wasenclosed in a plastic bag. The percentage difference between the firstand second set of wash load inertia sensing test results are illustratedin Table 1 below. Each of the measured values was determined on thebasis of averaging the result obtained from three consecutive wash loadinertia sensing tests.

In order to provide a robust detection of potential water entrapmentconditions, the controller 16 is programmed with a failure thresholdvalue that is stored in the memory device within the controller 16. Thisfailure threshold value sets a limit or trigger value as a limit abovewhich will provide an indication that water is entrapped within the spinbasket 13. It has been found that a failure threshold value in the orderof +3% will provide a suitable threshold value level to provide a watertrapped indication. Therefore, the results of the first and secondreference timing value comparison test are also compared with thethreshold value. If the threshold value is at or above 3% a waterentrapment condition is initiated and the spin speed limited to belowthe critical spin speed. Otherwise, the wash cycle will initiate anormal dehydration spin speed.

TABLE 1 WATER TRAPPED NORMAL LOAD LOAD SIZE AND TYPE LOAD (Plastic Bag)2 kg Cotton −5% +14% 3.3 kg Cotton −4% +18% 6.2 kg Cotton −3% +13% SmallSynthetic Items −10% +11% Med Synthetic Items −9% +12% 1 kg Towels −6% +9% 2 kg Towels −8% +13% 4 kg Towels −10% 0.16

Implementation

In order to prevent any water entrapment from affecting the wash cycleand providing a fault type condition, the wash load inertia sensingsystem of the present invention is programmed into the wash cyclesoftware residing in the controller 16. The wash load inertia sensingprocess steps are implemented each time an agitation cycle is completedand prior to a wash load dehydration spin cycle being undertaken. Thiswill limit the occurrence of potentially damaging off-balance conditionsoccurring and therefore limit the potential risk of damage to thewashing appliance 10.

The controller 16 will be programmed to detect small wash loads and assuch the wash load inertia sensing system will be disabled. Thiscondition will typically relate to a bowl float level that is measuredto be less than 120 mm. Disabling the wash load inertia sensing systemwill avoid any false fault trips when the bowl is empty or where the isvery little load in the washing machine 10.

The inertia sensing system is a multi-stage wash load inertia sensingsystem that is incorporated into and integral with a typical wash cycleset of events. The detection of a water entrapment condition preferablydoes not terminate a wash cycle and instead enables the wash cycle toresume and run to completion by limiting the spin speed at or below acritical speed level. In order to account for changing wash cycleconditions such as a power failure event or a user interrupting the washcycle for example, the controller 16 has been programmed to deal withsuch situations. Some of the possible scenarios are outlined below.

a. Clearing the “Water Trapped” Status

The ‘water trapped’ status is cleared once each particular phase of thewash cycle has completed. Furthermore, the ‘water trapped’ status isclear when the washing machine 10 commences a further agitation phase awash load inertia sensing cycle is undertaken before the wash cyclecommences another drain/spin phase.

b. Power Cut

When a ‘water trapped’ situation is sensed by the wash load inertiasensing system, the ‘water trapped’ data indication is saved in thememory device within the controller 16 in the ‘brown out data’ area.Data stored in the ‘brown out data’ area is used as reference valueinformation enabling this data to be retrieved once washing machinepower is restored. This will enable the wash cycle to restart the washcycle from the point where the washing machine 10 lost power.

c. Wash Load Sensing is Interrupted and the Wash Cycle is Advanced to aDifferent Stage.

The wash load inertia sensing system undertakes three distinct processsteps to test for a ‘water trapped’ condition. The first two inertiatest steps enable a reference ‘inertia’ value to be determined whilstthe last stage of the inertia sensing test compares a further measured‘inertia’ value with the reference ‘inertia’ value on completion of a330 rpm spin phase. If a user pauses or advances the wash cycle whilethe wash load inertia sensing process is being performed, the processstep count will be renumbered and the controller 16 will continue toundertake the remainder of the inertia sensing processing steps untilthe entire inertia sensing process has been competed.

d. Spray/Deep Rinse

Whilst it is not strictly necessary to perform inertia sensing duringthe spray rinse cycle after the main wash cycle as the machine is goingto fill up again in the deep rinse cycle. However, if the wash cycle isinterrupted during the spray rinse phase of the cycle and the wash cycleis advanced to a spin phase of the wash cycle, the wash load inertiasensing is performed for a mini aqua rinse cycle which is part of thespray portion of the deep rinse phase of the wash cycle.

Under normal operating conditions the washing machine will spin a washload up to a maximum of 1000 rpm for a predetermined period of timeallowing for a large amount of water to be removed from the wash load.In the event that a water entrapment condition is detected by thewashing machine, thereby limiting the spin speed to at or below acritical spin speed, water entrapped spin cycle will run for the sametime as that provided for normal spin operating conditions. As such, thewash load will be ‘wetter’ on completion of the ‘water trapped’ spinphase than if the wash load was spun at 1000 rpm. However, the level ofwetness is insignificant given the risks involved in running the washingmachine into an off-balance condition that will averted by implementingthe wash load inertia sensing system of the present invention.

1. A washing machine comprising: a cabinet, a wash tub supported withinthe cabinet; a spin basket for holding a wash load, the spin basketrotatable in the wash tub by a motor, a controller for driving the motorto rotate the spin basket, the controller adapted to detect waterentrapment within a wash load in a spin basket of a washing machine by:measuring a first parameter indicative of the rotational inertia of thespin basket when accelerated to a first spin speed, controlling the spinbasket to dewater a wash load in the spin basket, measuring a secondparameter indicative of the rotational inertia of the spin basket at thefirst speed, comparing the first and second parameters, and detectingwhether there is water entrapped in the wash load based on thecomparison between the first and second parameters.
 2. A washing machineaccording to claim 1 wherein if the controller detects that there iswater entrapped in the wash load, the controller operates the motor torotate the spin basket a second spin speed, and wherein the controllerdetects that there is no water entrapped in the wash load, thecontroller operates the motor to rotate the spin basket at a third spinspeed, the third spin speed being greater than the second spin speed. 3.A washing machine according to claim 1 wherein it is detected that thereis water entrapped if the rotational inertia indicated by the secondparameter is greater than the rotational inertia indicated by the firstparameter.
 4. A washing machine according to claim 1 wherein measuringthe first parameter comprises: a) the controller operating the motor toapply a torque to the spin basket to rotate spin basket at the firstspin speed, b) the controller operating the motor to remove the torqueand allow the spin basket to decelerate to an idle spin speed, and c)the controller measuring a first time for the spin basket to decelerateto the idle speed, wherein the measured first time is the firstparameter.
 5. A washing machine according to claim 4 wherein the step ofmeasuring the second parameter comprises: a) the controller operatingthe motor to apply a torque to the spin basket to rotate spill basket atthe first spin speed, b) the controller operating the motor to removethe torque and allow the spin basket to decelerate to a idle spin speed,and c) the controller measuring a second time for the spin basket todecelerate to the idle speed, wherein the measured second time is thesecond parameter,
 6. A washing machine according to claim 5 wherein itis detected that there is water entrapped if the second time is largerthan the first time.
 7. A washing machine according to claim 1 whereinthe step of measuring the first parameter comprises: a) the controlleroperating the motor to apply a torque to the spin basket to rotate spinbasket at the first spin speed, b) the controller operating the motor toremove the torque and allow the spin basket to decelerate to a idle spinspeed, c) the controller measuring a time for the spin basket todecelerate to the idle speed, d) the controller repeating steps a)-c) atleast once to obtain one or more additional measured times, and e) thecontroller calculating the average of the measured times, wherein theaverage of the measure times is the first parameter.
 8. A washingmachine according to claim 7 wherein the step of measuring the secondparameter comprises: a) the controller operating the motor to apply atorque to the spin basket to rotate spin basket at the first spin speed,b) the controller operating the motor to remove the torque and allow thespin basket to decelerate to a idle spin speed, c) the controllermeasuring a time for the spin basket to decelerate to the idle speed, d)the controller repeating steps a)-c) at least once to obtain one or moreadditional measured times, and e) the controller calculating the averageof the measured times, wherein the average of the measure times is thefirst parameter.
 9. A washing machine according to claim 1 wherein thefirst parameter indicative of the rotational inertia of the spin basketwhen accelerated to a first spin speed is the time taken for the spinbasket to decelerate from the first speed to an idle speed.
 10. Awashing machine according to claim 1 wherein the second parameterindicative of the rotational inertia of the spin basket when acceleratedto a first spin speed is the time taken for the spin basket todecelerate from the first speed to an idle speed.
 11. A washing machineaccording to claim 2 wherein the second spin speed is less 670 rpm. 12.A washing machine according to claim 2 wherein the third spin speed isgreater than 670 rpm.
 13. A washing machine according to claim 1 whereinthe first speed is between 15 rpm and 150 rpm.
 14. A washing machineaccording to any one of claims 4, 5, 7 or 8 wherein the idle speed isbetween 35 rpm and 0 rpm.
 15. A method of detecting water entrapmentwithin a wash load in a spin basket of a washing machine, comprising thesteps of: measuring a first parameter indicative of the rotationalinertia of the spin basket when accelerated to a first spin speed,dewatering the wash load, measuring a second parameter indicative of therotational inertia of the spin basket at the first speed, comparing thefirst and second parameters, and determining whether there is waterentrapped in the wash load based on the comparison between the first andsecond parameters.
 16. A method according to claim 15 wherein if it isdetermined that there is water entrapped in the wash load, rotating thespin basket a second spin speed, and wherein if it is determined thatthere is no water entrapped in the wash load, rotating the spin basketat a third spin speed, the third spin speed being greater than thesecond spin speed.
 17. A method according to claim 15 wherein it isdetermined that there is water entrapped if the rotational inertiaindicated by the second parameter is greater than the rotational inertiaindicated by the first parameter.
 18. A method according to claim 15wherein the step of measuring the first parameter comprises: a) applyinga torque to the spin basket to rotate spin basket at the first spinspeed, b) removing the torque and allowing the spin basket to decelerateto a idle spin speed, and c) measuring a first time for the spin basketto decelerate to the idle speed, wherein the measured first time is thefirst parameter.
 19. A method according to claim 18 wherein the step ofmeasuring the second parameter comprises: a) applying a torque to thespin basket to rotate spin basket at the first spin speed, b) removingthe torque and allowing the spin basket to decelerate to a idle spinspeed, and c) measuring a second time for the spin basket to decelerateto the idle speed, wherein the measured second time is the secondparameter,
 20. A method according to claim 19 wherein it is determinedthat there is water entrapped if the second time is larger than thefirst time.
 21. A method according to claim 15 wherein the step ofmeasuring the first parameter comprises: a) applying a torque to thespin basket to rotate spin basket at the first spin speed, b) removingthe torque and allowing the spin basket to decelerate to a idle spinspeed, c) measuring a time for the spin basket to decelerate to the idlespeed, d) repeating steps a)-c) at least once to obtain one or moreadditional measured times, and e) calculating the average of themeasured times, wherein the average of the measure times is the firstparameter.
 22. A method according to claim 21 wherein the step ofmeasuring the second parameter comprises: a) applying a torque to thespin basket to rotate spin basket at the first spin speed, b) removingthe torque and allowing the spin basket to decelerate to a idle spinspeed, c) measuring a time for the spin basket to decelerate to the idlespeed, d) repeating steps a)-c) at least once to obtain one or moreadditional measured times, and e) calculating the average of themeasured times, wherein the average of the measure times is the secondparameter.
 23. A method according to claim 15 wherein the firstparameter indicative of the rotational inertia of the spin basket whenaccelerated to a first spin speed is the time taken for the spin basketto decelerate from the first speed to an idle speed.
 24. A methodaccording to claim 15 wherein the second parameter indicative of therotational inertia of the spin basket when accelerated to a first spinspeed is the time taken for the spin basket to decelerate from the firstspeed to an idle speed.
 25. A method according to claim 16 wherein thesecond spin speed is less 670 rpm.
 26. A method according to claim 16wherein the third spin speed is greater than 670 rpm.
 27. A methodaccording to claim 15 wherein the first speed is between 15 rpm and 150rpm.
 28. A method according to any one of claims 18, 19, 21 or 22wherein the idle speed is between 35 rpm and 0 rpm.
 29. A methodaccording to any one of claims 18, 19, 21 or 22 wherein measuring afirst or second time for the spin basket to decelerate to an idle spinspeed comprises: measuring the time taken for the spin basket todecelerate from an intermediate spill speed between the first and idlespin speed to the idle spin speed.
 30. A washing machine according toany one of claims 4, 5, 7 or 8 wherein measuring a first or second timefor the spin basket to decelerate to an idle spin speed comprises:measuring the time taken for the spin basket to decelerate from anintermediate spin speed between the first and idle spin speed to theidle spin speed.
 31. A washing machine comprising: a cabinet, a wash tubsupported within the cabinet; a spin basket for holding a wash load, thespin basket rotatable in the wash tub by a motor, a controller fordriving the motor to rotate the spin basket, the controller adapted todetect water entrapment within a spin basket of a washing machine by:measuring a first parameter indicative of the rotational inertia of thespin basket when accelerated to a first spin speed, controlling the spinbasket to dewater a wash load in the spin basket, measuring a secondparameter indicative of the rotational inertia of the spin basket at thefirst speed, comparing the first and second parameters, and detectingwhether there is water entrapped in the wash load based on thecomparison between the first and second parameters.